The present invention relates generally to a new and improved fibrous nonwoven sheet material having sufficient wet strength to be used as a premoistened wipe. In some embodiments, the inventive sheet material is also capable of disintegrating into small pieces and individual fibers with mild agitation in moving water after a brief period of time and disposal in a sanitary waste system.
Nonwoven sheet material is commonly cut into individual wiping sheets. While the cut sheets may be used dry, more typically the individual sheets are saturated with a chemical solution suited for an intended end use, stacked and wrapped in a liquid tight package for subsequent dispensing. The chemical solution often includes bactericides and other biological control agents as well as emulsifiers, pH buffers, perfumes and the like. The liquid tight packaging maintains the saturated condition of the wiping sheet until use.
Such premoistened wiping sheets, also called wet wipes or simply, wipes, are commonly used by consumers for cleaning or wiping, particularly when wash water is not readily available or cannot be conveniently used. Travelers and parents of small children find such wipes especially convenient. These wipes are also useful for applying or removing makeup, cleansing parts of the body, as a substitute for conventional dry toilet paper and for household cleaning. A high wet tensile strength to resist tearing or puncturing of the premoistened wipe during dispensing and use is very desirable.
As will be appreciated, it is often desirable to dispose of used premoistened wipes through a sewer or septic system. Thus, while premoistened wipes must have sufficient wet strength to resist tearing and puncturing during vigorous use, they also must easily and readily break up into smaller pieces and fibers within the moving water present in a sanitary or septic system and preferably be substantially totally biodegradable.
Premoistened wipes or sheet material capable of breaking up within a septic system are known. Some wipes described heretofore have utilized a pH sensitive water-soluble binder or adhesive to achieve the requisite wet strength during packaging and use. The binders of such wipes exhibit a resistance to weakening during storage in a controlled pH solution, but are much more loosely bonded when the wipe has been immersed in a relatively large amount of turbulent, substantially neutral water. One such wet wipe is described in U.S. Pat. No. 4,117,187 to Adams et al. Such wipes typically work within a chemical solution having a limited pH range and are difficult to break up in other than the preferred, substantially neutral pH, environment.
Other sheet materials completely eliminate any binder system. These wipes rely solely on hydroentanglement of the fibers comprising the sheet material to achieve the strength required for processing and for one time use. Such sheet materials disentangle when exposed to agitation so that they can be disposed of in sewer and septic systems. A material of this type is described in U.S. Pat. No. 4,755,421 to Manning et al, the disclosure of which is incorporated herein by reference. That patent describes a binder free, hydroentangled web material consisting essentially of a blend of rayon fibers and papermaking pulp. While such materials exhibit acceptable absorption characteristics, the wet strength of such materials, particularly at low basis weights, has proven to be relatively poor. In fact, the present inventors have been unable to duplicate the results of Manning at basis weights below 55 grams per square meter.
Definitions
Bicomponent fibers—Fibers that have been formed from at least two polymers extruded from separate extruders through a single spinneret hole to form a single filament. The polymers are arranged in substantially constantly positioned distinct zones across the cross-section of the bicomponent fibers and extend continuously along the length of the bicomponent fibers. The configuration of such a bicomponent fiber may be, for example, a sheath/core arrangement wherein one polymer is surrounded by another or a side by side arrangement.
Cellulose fibers—Natural, e.g. non-manmade, cellulosic fibers from natural sources such as woody and non-woody plants. Woody plants include, for example, deciduous and coniferous trees. Non-woody plants include, for example, cotton, flax, esparto grass, sisal, abaca, milkweed, straw, jute, hemp, and bagasse.
Cross machine direction (CD)—The direction perpendicular to the machine direction.
Denier—A unit used to indicate the fineness of a filament given by the weight in grams for 9,000 meters of filament. A filament of 1 denier has a mass of 1 gram for 9,000 meters of length.
Lyocell—Manmade cellulose material obtained by the direct dissolution of cellulose in an organic solvent without the formation of an intermediate compound and subsequent extrusion of the solution of cellulose and organic solvent into a coagulating bath. As used herein, lyocell is distinguished from regenerated cellulose.
Machine direction (MD)—The direction of travel of the forming surface onto which fibers are deposited during formation of a nonwoven web material.
Non-thermoplastic material—Any material which does not fall within the definition of thermoplastic material.
Nonwoven fabric, sheet or web—A material having a structure of individual fibers which are interlaid, but not in an identifiable manner as in a knitted fabric. Nonwoven materials have been formed from many processes such as, for example; meltblowing, spunbonding and water laying processes. The basis weight of nonwoven fabrics is usually expressed in grams per square meter (gsm) and the fiber fineness is measured in denier.
Polymer—Generally includes, for example, homoplymers, copolymers, such as for example, block, graft, random and alternating copolymers, terpolymers, etc, and blends and modifications thereof. Furthermore, unless otherwise specifically limited, the term “polymer” includes all possible geometrical configurations of the material. These configurations include, for example, isotactic, syndiotactic and random symmetries.
Regenerated cellulose—Manmade cellulose obtained by chemical treatment of natural cellulose to form a soluble chemical derivative or intermediate compound and subsequent decomposition of the derivative to regenerate the cellulose. Regenerated cellulose includes spun rayon and regenerated cellulose processes include the viscose process, the cuprammonium process and saponification of cellulose acetate.
Tex—A unit used to indicate the fineness of a filament given by the weight in grams for 1,000 meters of filament. A filament of 1 tex has a mass of 1 gram for 1,000 meters of length.
Thermoplastic material—A polymer that is fusible, softening when exposed to heat and returning generally to its unsoftened state when cooled to room temperature. Thermoplastic materials include, for example, polyvinyl chlorides, some polyesters, polyamides, polyfluorocarbons, polyolefins, some polyurethanes, polystyrenes, polyvinyl alcohol, caprolactams, copolymers of ethylene and at least one vinyl monomer (e.g., poly (ethylene vinyl acetates), and acrylic resins.